Semiconductor structure and method making the same

ABSTRACT

The present disclosure provides a method for forming an integrated circuit (IC) structure. The method comprises providing a substrate including a conductive feature; forming aluminum (Al)-containing dielectric layer on the conductive feature; forming a low-k dielectric layer on the Al-containing dielectric layer; and etching the low-k dielectric layer to form a contact trench aligned with the conductive feature. A bottom of the contact trench is on a surface of the Al-containing dielectric layer.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experienced rapidgrowth. Technological advances in IC materials and design have producedgenerations of ICs where each generation has smaller and more complexcircuits than the previous generation. However, these advances haveincreased the complexity of processing and manufacturing ICs and, forthese advances to be realized, similar developments in IC processing andmanufacturing are needed. In the course of IC evolution, functionaldensity (i.e., the number of interconnected devices per chip area) hasgenerally increased while geometry size (i.e., the smallest component orline that can be created using a fabrication process) has decreased.This scaling down process generally provides benefits by increasingproduction efficiency and lowering associated costs.

In semiconductor technology, an integrated circuit pattern can be formedon a substrate using various processes including a photolithographyprocess, ion implantation, deposition and etch. Damascene processes areutilized to form multilayer copper interconnections including verticalinterconnection vias and horizontal interconnection metal lines. Duringa damascene process, trenches are formed in a dielectric material layer,copper or tungsten is filled in the trenches, then a chemical mechanicalpolishing (CMP) process is applied to remove excessive metal on thedielectric material layer and planarize the top surface. Studies andresearches have been conducted to search, new conductive, dielectricmaterials, and new process integration schemes for a betterinterconnection. New interconnection materials, such as integratingcopper metallurgy in place of traditional aluminum can be used to reducethe resistance component of the RC time delay. New insulating materialwith a lower dielectric constant (k) than the incumbent silicon dioxidecan be applied to reduce the capacitance component as well as cross-talkbetween conductive lines to minimize time delay and power dissipation.In addition, metal capping or silicide capping can be used to overcomethe reliability problem caused by the dimensions scaling down.

Although existing approaches have been generally serving their intendedpurposes, they have not been entirely satisfactory in all respects.Accordingly, a semiconductor structure including a cap layer and amethod making the same are needed.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isemphasized that, in accordance with the standard practice in theindustry, various features are not drawn to scale. In fact, thedimensions of the various features may be arbitrarily increased orreduced for clarity of discussion.

FIG. 1 illustrates a flowchart of a method to form an integrated circuit(IC) structure including an aluminum (Al)-containing dielectric layeraccording to some embodiments of the present invention.

FIGS. 2-7 are cross sectional views of an IC structure including anAl-containing dielectric layer during various fabrication stages usingthe method of FIG. 1, constructed according to various aspects of thepresent disclosure in one or more embodiments.

FIGS. 8-9 are some alternative embodiments of the IC structure having anAl-containing dielectric layer of FIG. 5 according to various aspects ofthe present disclosure.

FIG. 10 compares the reflectivity of the surface of the Cu layer in theIC structure with different capping schemes being exposed to N₂O plasmaaccording to some embodiments of the present disclosure.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof the invention. Specific examples of components and arrangements aredescribed below to simplify the present disclosure. These are, ofcourse, merely examples and are not intended to be limiting. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.Moreover, the formation of a first feature over or on a second featurein the description that follows may include embodiments in which thefirst and second features are formed in direct contact, and may alsoinclude embodiments in which additional features may be formedinterposing the first and second features, such that the first andsecond features may not be in direct contact.

FIG. 1 illustrates a flowchart of a method 100 to form an integratedcircuit (IC) structure including an aluminum (Al)-containing dielectriclayer according to some embodiments of the present invention. FIGS. 2-5are cross sectional views of an IC structure 200 including anAl-containing dielectric layer during various fabrication stages usingthe method 100 of FIG. 1, constructed according to various aspects ofthe present disclosure in one or more embodiments. The method 100 andthe IC structure 200 are collectively described below with reference toFIGS. 1-5. Additional steps can be provided before, during, and afterthe method 100, and some of the steps described can be replaced oreliminated for additional embodiments of the method. The discussion thatfollows illustrates various embodiments of the IC structure 200 that canbe fabricated according to the method 100 of FIG. 1.

Referring to FIGS. 1 and 2, the method 100 begins at step 102 byproviding a semiconductor substrate 202. The semiconductor substrate 202may include silicon (Si). Alternatively or additionally, the substrate202 may include other elementary semiconductor such as germanium (Ge).The substrate 202 may also include a compound semiconductor such assilicon carbide, gallium arsenic, indium arsenide, and indium phosphide.The substrate 202 may include an alloy semiconductor such as silicongermanium, silicon germanium carbide, gallium arsenic phosphide, andgallium indium phosphide. In some embodiments, the substrate 202includes an epitaxial layer. For example, the substrate 202 may have anepitaxial layer overlying a bulk semiconductor. In some embodiments, thesubstrate 202 may include a semiconductor-on-insulator (SOI) structure.For example, the substrate 202 may include a buried oxide layer formedby a process such as separation by implanted oxygen or other suitabletechnique, such as wafer bonding and grinding.

The substrate 202 may also includes various p-type doped regions and/orn-type doped regions, implemented by a process such as ion implantationand/or diffusion. Those doped regions include n-well, p-well, lightdoped region (LDD), heavily doped source and drain (S/D), and variouschannel doping profiles configured to form various integrated circuit(IC) devices, such as a complimentary metal-oxide-semiconductorfield-effect transistor (CMOSFET), imaging sensor, and/or light emittingdiode (LED). The substrate 202 may further include other functionalfeatures such as a resistor or a capacitor formed in and on thesubstrate. In some embodiments, the substrate 202 may further includelateral isolation features provided to separate various devices formedin the substrate 202. The isolation features may include shallow trenchisolation (STI) features to define and electrically isolate thefunctional features. In some examples, the isolation regions may includesilicon oxide, silicon nitride, silicon oxynitride, an air gap, othersuitable materials, or combinations thereof. The isolation regions maybe formed by any suitable process. The various IC devices may furtherinclude other features, such as silicide disposed on S/D and gate stacksoverlying channels.

The IC structure 200 may also include a plurality of dielectric layersand conductive features integrated to form an interconnect structureconfigured to couple the various p-type and n-type doped regions and theother functional features (such as gate electrodes), resulting afunctional integrated circuit. In some embodiments, the substrate 202may include a portion of the interconnect structure and is collectivelyreferred to as the substrate 202.

As noted above, the IC structure 200 includes an interconnect structure.The interconnect structure includes a multi-layer interconnect (MLI)structure and an inter-level dielectric (ILD) integrated with the MLIstructure, providing an electrical routing to couple various devices inthe substrate 202 to the input/output power and signals. Theinterconnect structure includes various metal lines, contacts and viafeatures (or via plugs). The metal lines provide horizontal electricalrouting. The contacts provide vertical connection between the substrate202 and metal lines while via features provide vertical connectionbetween metal lines in different metal layers.

As shown in FIG. 2, the IC structure 200 includes a conductive feature208. In some embodiments, the conductive feature 208 may include a metalcontact, a metal via, or a metal line. In some embodiments as shown inFIG. 2, the conductive feature 208 may be further surrounded by abarrier layer 206 to prevent diffusion and/or provide material adhesion.In some examples, the conductive feature 208 may include aluminum (Al),copper (Cu) or tungsten (W). The barrier layer 206 may include titaniumnitride (TiN), tantalum nitride (TaN), tungsten nitride (WN), titaniumsilicon nitride (TiSiN) or tantalum silicon nitride (TaSiN). Theconductive feature 208 and the barrier layer 206 may be formed by aprocedure including lithography, etching and deposition. In anotherembodiment, the conductive feature 208 includes an electrode of acapacitor, a resistor or a portion of a resistor. Alternatively, theconductive feature 208 includes a doped region (such as a source or adrain), or a gate electrode. In another example, the conductive feature208 includes a silicide feature disposed on respective source, drain orgate electrode. The silicide feature may be formed by a self-alignedsilicide (salicide) technique.

Still referring to FIGS. 1 and 2, the method 100 proceeds to step 104 byforming a cap layer 210 on the conductive feature 208. In someembodiments, the conductive feature 208 includes Cu, and the cap layerincludes a cobalt (Co) cap layer. In some alternative embodiments, thecap layer includes at least one layer of manganese (Mn), nickel (Ni),ruthenium (Ru), titanium (Ti) and/or combinations thereof. The cap layer210 may be deposited using any suitable method, such as chemical vapordeposition (CVD) or atomic layer deposition (ALD). In some embodiments,the cap layer 210 may have a thickness in a range from about 5 Å toabout 100 Å. In the present embodiment, the cap layer 210 is selectivelygrown on the conductive feature 208, but not the substrate 202, forcapping the conductive feature 208, such as Cu line. Therefore, the caplayer 210 is self-aligned with the conductive feature 208, as shown inFIG. 2. The cap layer 210 may be formed using a metal precursor, such asCo included precursor. In some embodiments, the Co included precursorincludes at least one of bis(cyclopentadienyl)cobalt(II) (Co(C₅H₅)₂),bis(ethylcyclopentadienyl)cobalt(II) (C₁₄H₁₈Co),bis(pentamethylcyclopentadienyl)cobalt(II) (C₂₀H₃₀Co),dicarbonylcyclopentadienyl cobalt(I) (C₅H₅Co(CO)₂), or cobalt carbonyl(Co₂(CO)₈). The cap layer 210 may effectively reduce the contactresistance and avoid the electromigration between different layers ofinterconnect structures. The cap layer 210 may also provide a goodintrinsic adhesion between the conductive feature 208 and the subsequentlayers formed on the conductive feature, such as etch stop layer (ESL),so that the material integration of the IC structure 200 can beimproved.

Referring to FIGS. 1 and 3, method 100 proceeds to step 106 by formingan aluminum (Al)-containing dielectric layer 212 on the cap layer 210.The Al-containing dielectric layer 212 may be formed to cover both thecap layer 210 and the part of the substrate 202 that is not covered bythe cap layer 210 as shown in FIG. 4. In some embodiments, theAl-containing dielectric layer 212 includes aluminum (Al), oxygen (O),nitrogen (N) and/or combinations thereof. In some embodiments, theAl-containing dielectric layer 212 includes Al with a composition in arange from about 5 wt % to about 20 wt %. In some embodiments, theAl-containing dielectric layer 212 includes 0 with a composition in arange from about 60 wt % to about 80 wt %. In some embodiments, theAl-containing dielectric layer 212 includes N with a composition in arange from about 10 wt % to about 30 wt %. In a preferable embodiment,the Al-containing dielectric layer 212 includes about 10 wt % of Al,about 70 wt % of 0, and about 20 wt % of N. The thickness of theAl-containing dielectric layer 212 may be controlled to have high enoughetching selectivity over the low-k dielectric layer during a plasmaetching process, and high enough etching selectivity over the ESL duringa wet etching process. Meanwhile, the thickness of the Al-containingdielectric layer 212 may also be controlled to have low enough contactresistance. In some embodiments, the Al-containing dielectric layer 212may have a thickness in a range from about 5 Å to about 30 Å.

In some embodiments, the Al-containing dielectric layer 212 may beformed using a CVD or an ALD process. The precursor used to form theAl-containing dielectric layer includes an Al included organic chemical,such as trimethylaluminium (TMA). In some embodiments, the formation ofthe Al-containing dielectric layer 212 starts with a pretreatmentprocess using NH₃ plasma, where the deposition chamber becomes a reducedenvironment including N free radical. Then the Al included precursor isimported and the Al from the precursor can be bonded with the N. The Alfrom the precursor may also adsorb oxygen (O) that is attached to thesurface of the cap layer 210, such as the surface oxidation layer of Cocap layer. In some embodiments, the NH₃ plasma treatment and the importof the Al included precursor are carried out for more than one cycle fordepositing the Al-containing dielectric layer 212 including Al, O, andN.

In some embodiments during the deposition of the Al-containingdielectric layer, the chamber pressure is in a range from about 0.1 torrto about 100 torr. The radio frequency (RF) power is in a range fromabout 10 W to about 1000 W. The flow rate of NH₃ is in a range fromabout 50 sccm to about 5000 sccm. The deposition temperature is in arange from about 150° C. to about 400° C. In some preferableembodiments, the Al-containing dielectric layer 212 of the presentinvention is deposited at chamber pressure in a range from about 1 torrto about 10 torr. In some embodiments, the RF power for the depositionis in a range from about 200 W to about 1000 W. In some embodiments, theNH₃ gas flow rate is in a range from about 100 sccm to about 1000 sccm.In some embodiments, the deposition temperature is in a range from about200° C. to about 400° C. In a preferable embodiment of the presentdisclosure, the Al-containing dielectric layer is deposited at a chamberpressure of about 3 torr, a RF power at about 600 W, a NH3 gas flow rateof about 500 sccm, and a deposition temperature of about 350° C. In someembodiments, the Al-containing dielectric layer 212 formed using a CVDor an ALD process has a porous structure with low density. In someembodiments, the reflectivity index (RI) of the Al-containing dielectriclayer is in the range from about 1.76 to about 1.80.

In some embodiments, Al-containing dielectric layer 212 has a highetching selectivity over the low-k dielectric layer during a plasmaetching process to form contact trenches. The Al-containing dielectriclayer 212 may also have high etching selectivity over the ESL during awet etching process to etch the ESL in the contact regions. The porousstructure of the Al-containing dielectric layer 212 may enable theelectron tunneling and/or the diffusion of the conductive feature (e.g.,Cu) between two adjacent interconnect levels, so that the Al-containingdielectric layer can reduce the contact resistance of the IC structure.In addition, the Al-containing dielectric layer 212 may effectivelyprevent the cap layer 210 and/or the conductive feature 208 from beingoxidized by the oxygen included plasma in the following process.

Referring to FIGS. 1 and 4, method 100 proceeds to step 108 by formingan etch stop layer (ESL) 214 on the Al-containing dielectric layer 212.In some embodiments, the ESL 214 includes a dielectric material chosento have etching selectivity for proper etch process at subsequentprocesses to form contact trenches. In some embodiments, the ESL 214 maybe deposited using any suitable technique, such as CVD, physical vapordeposition (PVD), ALD, or an epitaxial growing process. In someembodiments, the ESL 214 includes a silicon nitride (Si₃N₄) layer, anitrogen (N) doped silicon carbide (SiC) layer, and/or combinationsthereof. The ESL 214 may have a thickness in a range from about 50 Å toabout 200 Å. In some embodiments, the ESL 214 is formed using materialsincluding silane (SiH₄) and ammonia (NH₃) plasma. In some embodiments,the ESL 214 may have a dielectric constant (k) that is greater thanabout 5.5. The ESL 214 may have a higher density than the Al-containingdielectric layer 212. The ESL 214 may also have a lower etchingselectivity than the Al-containing dielectric layer 212 during theetching process of the low-k dielectric layer to form contact trenchesas discussed later in the following process. In some embodiments, theESL 214 may be formed to cover the Al-containing dielectric layer 212 asshown in FIG. 3.

In some embodiments, with the formation of the Al-containing dielectriclayer 212 in the present disclosure, the ESL 215 (of FIG. 8) may includea dielectric material that has a dielectric constant (k) less than about5. In some embodiments, the ESL 215 includes nitrogen (N) doped siliconcarbide (SiC), oxygen (O) doped SiC, and/or combinations thereof. Insome embodiments, the ESL 215 may be formed using silane (SiH₄), and aplasma gas including CO₂, N₂O or combinations thereof. In someembodiments, the thickness of the ESL 215 is in a range from about 10 Åto about 100 Å, as discussed later with reference to FIG. 8 in thisdisclosure. In some alternative embodiments, with the Al-containingdielectric layer 212 formed in the IC structure 200, the ESL may not beneeded, as discussed later with reference to FIG. 9 in this disclosure.

Still referring to FIGS. 1 and 4, method 100 may proceed to an optionalstep 110 to form a dielectric layer 216 on the ESL 214. In someembodiments, the dielectric layer 216 may include a silicon oxide (SiO₂)layer configured to block gas generated from the ESL 214 from getting incontact with the photoresist material that is used to pattern thesubsequent layers. Because the ESL 214 may include nitrogen (N), the ESL214 may generate NH₃ gas during outgassing, and the NH₃ gas may diffuseto the photoresist layer to react with the photoresist layer, causingthe photoresist layer to fail to be sensitive to the photons during thelithography process. Therefore, a SiO₂ layer 216 may be used to blockthe NH₃ outgassing from the ESL 214 to be in contact with thephotoresist layer. In some alternative embodiments, the dielectric layer216 may not be needed, as discussed later in this disclosure withreference to FIGS. 8-9.

Still referring to FIGS. 1 and 4, method 100 may proceed to step 112 byforming a low-k dielectric layer 218 over the Al-containing dielectriclayer 212. In some embodiments, the low-k dielectric layer 218 mayinclude one or more materials selected from the group consisting offluorinated silica glass (FSG), carbon doped silicon oxide, BlackDiamond® (Applied Materials of Santa Clara, Calif.), Xerogel, Aerogel,amorphous fluorinated carbon, Parylene, BCB (bis-benzocyclobutenes),SiLK (Dow Chemical, Midland, Mich.), polyimide, other suitablematerials, and combinations thereof. In some embodiments, the low-kdielectric layer 218 includes an extreme low-k dielectric material(XLK). In some embodiments, the low-k dielectric layer 218 includes aporous version of an existing Dow Corning dielectric material called FOX(flowable oxide) which is based on hydrogen silsesquioxane. A process offorming the low-k dielectric layer 218 may utilize spin-on coating orCVD. In some embodiments, a chemical mechanical polishing (CMP) processmay be used to further planarize the top surface of the low-k dielectriclayer 218.

Referring to FIGS. 1 and 5, method 100 proceeds to step 114 by etchingthe low-k dielectric layer 218 to form a contact trench 220. In someembodiments, the contact trench 220 may be formed by a lithographyprocess and an etching process including one or more etching steps. Thelithography process is used to pattern the low-k dielectric layer 218,and the etching process is applied to etch the low-k dielectric layer218 to expose the contact regions. In some embodiments, the etchingprocess includes an etch step using a plasma etch with a suitableetchant, such as a fluorine-containing etchant, to selectively etch thelow-k dielectric layer 218 without damaging to the conductive feature208. In some alternative embodiments, the etching process includes afirst etch step to remove the low-k dielectric layer 218 in the contactregions using a dry etch process with difluoromethane (CH₂F₂) plasma.The first etch step may stop at the ESL 214 so that the ESL 214 canprotect the substrate 202, the conductive feature 208 and the cap layer210, from being damaged during the first etch step. Then a second etchstep is used to selectively remove the ESL 214 in the contact regionsusing a wet etch with a suitable etchant, such as a hot phosphorous(H₃PO₄) acid. The second etching step may stop at the Al-containingdielectric layer 212, so that the Al-containing dielectric layer 212 canprotect the substrate 202 or the lower level interconnect features,including the conductive feature 208 or the cap layer 210, from beingdamaged during the second etch step. In some embodiments, theAl-containing dielectric layer 212 includes a dielectric material havinghigh selectivity over the ESL 214 in the second etch step. Therefore,the formation of the Al-containing dielectric layer 212 may effectivelyreduce or eliminate the damage to the lower level interconnect feature,such as the contact feature 208.

Referring to FIGS. 1 and 6, method 100 proceeds to step 116 by forming abarrier layer 222 along the wall of the contact trench 220. The barrierlayer 222 may also be formed on the top surface of the Al-containingdielectric layer 212 exposed in the contact trench 220. In someembodiments, the barrier layer 222 includes metal and is electricallyconductive but does not permit inter-diffusion and reactions between thelow-k dielectric layer 218 and the metal layer to be filled in thecontact trench 220. The barrier layer 222 may include refractory metalsand their nitrides. In various examples, the barrier layer 222 includesone or more materials selected from the group consisting of TiN, TaN,Co, WN, TiSiN, TaSiN, and combinations thereof. In some embodiments, thebarrier layer 222 may include multiple films. For example, Ti and TiNfilms may be used as the barrier layer 222. In some embodiments, thebarrier layer 222 may be deposited by PVD, CVD, metal-organic chemicalvapor deposition (MOCVD), ALD, other suitable techniques, orcombinations thereof.

Still referring to FIGS. 1 and 6, method 100 proceeds to step 118 bydepositing a metal layer 224 on the barrier layer 222 to fill thecontact trench 220. In some embodiments, the metal layer 224 may includecopper (Cu), aluminum (Al), tungsten (W) or other suitable conductivematerial. In some embodiments, the metal layer 224 may also include Cuor Cu alloy, such as copper magnesium (CuMn), copper aluminum (CuAl) orcopper silicon (CuSi). In some embodiments, the metal layer 224 may bedeposited by PVD. In some examples, the metal layer 224 may include Cu,and the Cu layer 224 may be formed by depositing a Cu seed layer usingPVD, and then forming a bulk Cu layer by plating. In some embodiments,the metal layer 224 may include a metal contact, a metal via, or a metalline. After the deposition of the metal layer 224, a chemical mechanicalpolishing (CMP) process may be performed to remove excessive metal layer224. A substantially coplanar top surface of the metal layer 224 and thelow-k dielectric layer 218.

Referring to FIGS. 1 and 6, method 100 proceeds to step 120 by formingan upper cap layer 226 on the metal layer 224. The method and the uppercap layer 226 formed at step 120 may be substantially similar to that ofstep 104. Referring to FIGS. 1 and 7, method 100 proceeds to step 122 byforming an upper Al-containing dielectric layer 228 on the upper caplayer 226. The method and the Al-containing dielectric layer 228 formedat step 122 may be substantially similar to that of step 106.

FIGS. 8-9 illustrate some alternative embodiments of the IC structure200 having an Al-containing dielectric layer of FIG. 5 according tovarious aspects of the present disclosure. In some embodiments as shownin FIG. 8, the ESL 215 may include materials with dielectric constantthat is lower than about 5, such as N doped SiC and/or O doped SiC. Thethickness of the ESL 215 may be in a range from about 10 Å to about 100Å, and the dielectric layer 216 may not be necessary in the IC structure200. The formation of the ESL 215 may include using CO₂ or N₂O plasma.The CO₂ or N₂O plasma may oxidize the cap layer 210 and/or theconductive feature 208. In some embodiments, the formation of thecontact trenches in the IC structure 200 of FIG. 8 may include anetching process including more than one step. For example, the etchingprocess includes a first etch step to etch the low-k dielectric layer218 in the contact regions. The first etch step may include a dry etchusing difluoromethane (CH₂F₂) plasma, and the first etch step stops atthe ESL 215. Then a second etch step is used to selectively remove theESL 215 in the contact regions using a wet etch with a suitable etchant,such as a hot phosphorous (H₃PO₄) acid. The second etching stepselectively removes the ESL 215 in the contact regions and stops at theAl-containing dielectric layer 212. Therefore, the Al-containingdielectric layer 212 may protect the substrate 202 or the lower levelinterconnect features, including the conductive feature 208 or the caplayer 210, from being damaged during the contact trench etching process.As discussed earlier in the present disclosure, the Al-containingdielectric layer 212 may effectively prevent the cap layer 210 and/orthe conductive feature 208 from being oxidized by the CO₂ or N₂O plasma.

In some alternative embodiments as shown in FIG. 9, neither the ESL 215nor the dielectric layer 216 is necessary in the IC structure 200 whenthe IC structure includes an Al-containing dielectric layer 212. In someembodiments, the formation of the contact trenches in the IC structure200 of FIG. 9 may include a one-step etching process using a plasma etchwith a suitable etchant, such as a fluorine-containing etchant, toselectively etch the low-k dielectric layer 218 in the contact regionswithout damaging the Al-containing dielectric layer 212 or theconductive feature 208. This is due to the high etching selectivity ofthe Al-containing dielectric layer 212 over the low-k dielectric layer218, so that the contact trench etching process may stop at theAl-containing dielectric layer 212. In addition, the Al-containingdielectric layer 212 may effectively prevent the cap layer 210 and/orthe conductive feature 208 from being oxidized. In some alternativeembodiments, the IC structure including the Al-containing dielectriclayer may also eliminate the cap layer 210, leaving the Al-containingdielectric layer 212 as the interfacial layer between the upper leveland the lower level of the interconnect structure.

FIG. 10 compares the reflectivity of the surface of the Cu layer in theIC structure with different capping schemes when exposed to N₂O plasmaaccording to some embodiments of the present disclosure. As shown inFIG. 10, the pure Cu without any capping layer or the Cu with only Cocapping layer demonstrate obvious oxidation effect, as evidenced by thereduced reflectivity of the surface of the Cu layer. The reducedreflectivity can be caused by the formation of the copper oxide layer onthe surface of the Cu layer. When the Cu layer is covered with theAl-containing dielectric layer 212 as discussed in the presentdisclosure (e.g., FIG. 7, FIG. 8, or FIG. 9), the Cu layer maintains itshigh reflectivity as shown in FIG. 10. FIG. 10 shows an effectiveanti-oxidation capability of the Al-containing dielectric layer, whichcould prevent the surface of the Cu layer from being oxidized by theoxygen included plasma (e.g., CO₂ or N₂O plasma).

An IC structure without the Al-containing dielectric layer may result inan over etching problem. The over etching can result in an increasedcontact resistance from the upper level to the lower level in theinterconnect structure, and can affect the reliability performance ofthe IC structure and the final device. Although not intended to belimiting, the present disclosure provides one or more benefits. TheAl-containing dielectric layer included in the IC structure as discussedin the present disclosure can effectively prevent the over etchingduring the contact trench etching process due to the high etchingselectivity of the Al-containing dielectric. The Al-containingdielectric layer can also effectively reduce the capacitance and providean improved reliability performance as the dimension of the IC structurescales down.

The present disclosure provides a method for forming an integratedcircuit (IC) structure. The method includes providing a substrateincluding a conductive feature; forming an aluminum (Al)-containingdielectric layer on the conductive feature; forming a low-k dielectriclayer on the Al-containing dielectric layer; and etching the low-kdielectric layer to form a contact trench aligned with the conductivefeature. A bottom of the contact trench is on a surface of theAl-containing dielectric layer.

In some embodiments, the method further includes forming a cap layerbetween the conductive feature and the Al-containing dielectric layer. Awidth of the cap layer is substantially similar to a width of theconductive feature. The forming the cap layer may include selectivelydepositing at least one layer of Co, Mn, Ni, Ru, or Ti to be alignedwith the conductive feature.

In some embodiments, the method further includes forming an etch stoplayer (ESL) between the Al-containing dielectric layer and the low-kdielectric layer; and etching the ESL to form the contact trench. Theforming the ESL may include depositing a layer including at least one ofN doped SiC layer or O doped SiC layer using a plasma gas, the plasmagas including at least one of CO₂ or N₂O. The forming the ESL mayinclude depositing a layer including at least one of N doped SiC layeror Si₃N₄ layer using silane (SiH₄) and NH₃ plasma. The etching the low-kdielectric layer may include a dry etch process using afluorine-containing etchant. The etching the ESL may include a wet etchprocess which stops at the Al-containing dielectric layer. In someembodiments, the method further includes forming a dielectric layerbetween the ESL and the low-k dielectric layer; and etching thedielectric layer to form the contact trench.

In some embodiments, the forming the Al-containing dielectric layerincludes performing a NH₃ plasma treatment; importing an Al-containingorganic precursor; and depositing the Al-containing dielectric layerincluding Al, N and O. The Al-containing dielectric layer is formedusing a process selected from the group consisting of chemical vapordeposition (CVD), atomic layer deposition (ALD), and a combinationthereof. The forming the Al-containing dielectric layer may includedepositing the Al-containing dielectric layer using a chamber pressurein a range from about 0.1 torr to about 100 torr. The forming theAl-containing dielectric layer may include depositing the Al-containingdielectric layer using a RF power in a range from about 10 W to about1000 W. The forming the Al-containing dielectric layer may includedepositing the Al-containing dielectric layer at a temperature in arange from about 150° C. to about 400° C. The forming the Al-containingdielectric layer may include depositing the Al-containing dielectriclayer using a flow rate of the NH₃ plasma in a range from about 50 sccmto about 5000 sccm.

The present disclosure also provides a method for forming an integratedcircuit (IC) structure. The method includes providing a substrateincluding a conductive feature; forming a cap layer on the conductivefeature; forming an aluminum (Al)-containing dielectric layer on the caplayer; forming an etch stop layer (ESL) on the Al-containing dielectriclayer; forming a low-k dielectric layer on the ESL; and etching thelow-k dielectric layer and the ESL to form a contact trench aligned withthe conductive feature. A bottom of the contact trench is on a surfaceof the Al-containing dielectric layer.

In some embodiments, the etching the low-k dielectric layer and the ESLincludes dry etching the low-k dielectric layer using afluorine-containing etchant, and wet etching the ESL using a hotphosphorous acid (H₃PO₄). The wet etching the ESL stops at theAl-containing dielectric layer.

The present disclosure also provides yet another embodiment of anintegrated circuit (IC) structure. The IC structure comprises asubstrate including a first conductive feature; a cap layer formed onthe conductive feature and aligned with the first conductive feature; analuminum (Al)-containing dielectric layer disposed on the cap layer; anetch stop layer (ESL) disposed on the Al-containing dielectric layer; alow-k dielectric layer disposed on the ESL; and a second conductivefeature filling a contact trench formed through the low-k dielectriclayer and the ESL. The second conductive feature is aligned with thefirst conductive feature. The Al-containing dielectric layer is insertedbetween the cap layer on the first conducive feature and the secondconductive feature. A width of the cap layer is substantially similar toa width of the first conductive feature. The Al-containing dielectriclayer is formed to cover the cap layer and the substrate.

In some embodiments, a thickness of the ESL is in a range from about 10Å to about 200 Å. The Al-containing dielectric layer may include Al, Nand O. A thickness of the Al-containing dielectric layer is in a rangefrom about 5 Å to about 30 Å.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method for forming an integrated circuit (IC)structure, comprising: providing a substrate including a firstconductive feature; forming a cap layer on the first conductive featuresuch that a width of the cap layer is substantially similar to a widthof the first conductive feature, wherein the cap layer includes at leastone metal from the group consisting of: Co, Mn, Ni, Ru, and Ti; formingan Al-containing dielectric layer on the cap layer, wherein theAl-containing dielectric layer extends beyond the cap layer and thefirst conductive feature horizontally, and wherein the Al-containingdielectric layer includes: Al with a composition in a range from about 5wt % to about 20 wt %, O with a composition in a range from about 60 wt% to about 80 wt %, and N with a composition in a range from about 10 wt% to about 30 wt %; forming a low-k dielectric layer on theAl-containing dielectric layer; etching the low-k dielectric layer toform a contact trench aligned with the first conductive feature, whereina bottom of the contact trench is on a surface of the Al-containingdielectric layer; and forming a second conductive feature in the contacttrench, wherein the first conductive feature is coupled to the secondconductive feature by the Al-containing dielectric layer.
 2. The methodof claim 1, further comprising: forming an etch stop layer (ESL) betweenthe Al-containing dielectric layer and the low-k dielectric layer; andetching the ESL to form the contact trench.
 3. The method of claim 2,wherein the forming the ESL includes depositing a layer including atleast one of a nitrogen-doped SiC layer or an oxygen-doped SiC layer,wherein the depositing of the layer is performed using a plasma gas, theplasma gas including at least one of CO₂ or N₂O.
 4. The method of claim2, wherein the forming the ESL includes depositing a layer including atleast one of a nitrogen-doped SiC layer or a Si₃N₄ layer.
 5. The methodof claim 2, wherein the etching the low-k dielectric layer includes adry etch process using a fluorine-containing etchant, and wherein theetching the ESL includes a wet etch process which stops at theAl-containing dielectric layer.
 6. The method of claim 2, furthercomprising: forming a dielectric layer between the ESL and the low-kdielectric layer; and etching the dielectric layer to form the contacttrench.
 7. The method of claim 1, wherein the forming the Al-containingdielectric layer includes: performing a NH₃ plasma treatment; importingan Al-containing organic precursor; and depositing the Al-containingdielectric layer including Al, N and O.
 8. The method of claim 7,wherein the Al-containing dielectric layer is formed using a processselected from the group consisting of chemical vapor deposition (CVD),atomic layer deposition (ALD), and a combination thereof.
 9. The methodof claim 8, wherein the forming the Al-containing dielectric layerincludes: depositing the Al-containing dielectric layer using a chamberpressure in a range from about 0.1 ton to about 100 torr.
 10. The methodof claim 8, wherein the forming the Al-containing dielectric layerincludes: depositing the Al-containing dielectric layer using a RF powerin a range from about 10 W to about 1000 W.
 11. The method of claim 8,wherein the forming the Al-containing dielectric layer includes:depositing the Al-containing dielectric layer at a temperature in arange from about 150° C. to about 400° C.
 12. The method of claim 8,wherein the forming the Al-containing dielectric layer includes:depositing the Al-containing dielectric layer using a flow rate of theNH₃ plasma in a range from about 50 sccm to about 5000 sccm.
 13. Themethod of claim 1, wherein the Al-containing dielectric layer has asubstantially planar bottom surface directly over the first conductivefeature that extends beyond the first conductive feature horizontally.14. A method for forming an integrated circuit (IC) structure,comprising: providing a substrate including a first conductive feature;forming a cap layer on the first conductive feature, a width of the caplayer being substantially similar to a width of the first conductivefeature; forming an Al-containing dielectric layer on the cap layer,wherein the Al-containing dielectric layer has a substantially planarbottom surface on the cap layer that extends beyond the cap layer andthe first conductive feature horizontally, and wherein the Al-containingdielectric layer is formed with a thickness in a range from about 5angstroms to about 30 angstroms; forming an etch stop layer (ESL) on theAl-containing dielectric layer; forming a low-k dielectric layer on theESL; etching the low-k dielectric layer and the ESL to form a contacttrench aligned with the first conductive feature, wherein a bottom ofthe contact trench is on a surface of the Al-containing dielectriclayer; and forming a second conductive feature on the Al-containingdielectric layer directly above the first conductive feature.
 15. Themethod of claim 14, wherein the etching the low-k dielectric layer andthe ESL includes: dry etching the low-k dielectric layer using afluorine-containing etchant, and wet etching the ESL using a hotphosphorous acid (H₃PO₄), wherein wet etching the ESL stops at theAl-containing dielectric layer.
 16. A fabrication method comprising:receiving a substrate having a first conductive feature disposedthereupon; forming a capping layer containing a first metal on the firstconductive feature; forming a porous dielectric layer containing asecond metal on the capping layer, wherein the second metal is differentfrom the first metal, wherein the porous dielectric layer has asubstantially planar bottom surface over the capping layer and the firstconductive feature that extends beyond the first conductive feature;forming an interconnect dielectric layer on the porous dielectric layer;and forming a second conductive feature within the interconnectdielectric layer, wherein the second conductive feature is coupled tothe first conductive feature by the porous dielectric layer.
 17. Themethod of claim 16, wherein the first metal includes at least one of Co,Mn, Ni, Ru, or Ti, and wherein the second metal includes aluminum. 18.The method of claim 16 further comprising: forming an etch-stop layer onthe porous dielectric layer such that the interconnect dielectric layeris disposed on the etch-stop layer, wherein the etch-stop layer has adifferent composition than the porous dielectric layer and theinterconnect dielectric layer.
 19. The method of claim 16, wherein thefirst conductive feature includes a barrier layer and a conductive fillmaterial disposed within the barrier layer.